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Clinical relevant anatomy

The acetabulum is formed by an anterior and a posterior column of the bone. The posterior column; which extends from the ischiopubic ramus up to the ilium, including the greater and lesser sciatic notch, most of the quadrilateral plate and ischial tuberosity. Then we have the anterior column; which comprises the superior pubic ramus , the entire pelvic brim, the anterior wall of the os coxae and the iliac wing. The socket is thus a fusion of iliuum, ischium and pubis[1].

Epidemiology

Acetabulum fractures are less common and occur with an incidence of about three per 100.000 population[2]. An acetabular fracture is mostly caused by a traumatic accident, such as a motor vehicle or a bad fall, and affects often the younger population. These kind of fractures are uncommon in elderly patients, but lately the number is increasing. The osteoporosis of the bone makes the bone vulnerable and can cause an acetabulum fracture from a simple low fall [3].

A fracture of the acetabulum can be associated with late morbidity referable to the development of osteoarthritis[4][5].The force exerted by this high impact fall drives the femoral head into the acetabulum like a hammer.For this reason, other musculoskeletal injuries can’t be overlooked, f.e. fractures of the knee and sciatic nerve lesion are possible co-injuries. Also the damage to the articular surface must be suspected[6].

Diagnostic procedures

There are various numbers of fracture patterns in the acetabulum. For the classification of these fractures, the Judet-Letournel classification is most accepted system. The five most common fractures, representative for 90% of all, are[1]:

1) Both'column': This is a fracture that involves the anterior and posterior column and extends through the obturator ring. The characteristic for this fracture is the spur sign. It is a sign that represents the displacement of the fracture involving sciatic buttress. When this is present, the acetabulum can no longer carry the weight of the upper body.

2) Transverse: This fracture involves both anterior and posterior column. This means that the iliopectineal and ilioischial lines of the pelvis are discontinue.

3)T-shaped: Similar to the transverse fractures, the difference is that the T-shaped also extends inferiorly into the obturator ring. What differentiates it from the both column fracture is that the fracture doesn’t involve the extension to the iliac wing.

4) 'Transverse' with posterior wall: This is a transverse fracture only there is also a comminution of the posterior wall.

5)Isolated 'posterior 'wall: One of the most common acetabulum fractures with a preponderance of 27 %. The posterior wall in this fracture is comminuted. The iliopectineal line is not disrupted but the ilioischial line may be [7][1][8].

The force and the position of the femur head at the time of impact is one of the determination factors of a specific type of fracture.The following guidelines are made use of: [7]

Head of femur

When the head of the femur is in exorotation: the anterior part of the acetabulum gets disrupted.

When the head of the femur is in endorotation: the posterior part of the acetabulum gets disrupted or T-shaped fracture depending on the degree of endorotation.

When the head of the femur is in adduction: Transverse or T-shaped fracture occur, because the superolateral area is affected.

When the head of the femur is in abduction: Transverse or T-shaped fracture, because the inferomedial area is gets touched[7]

When the hip is flexed (90°)and knee flexed or extended : Posterior column fracture occurs; This is similar in both positions of the knee.Another variable that must be considered is the size of an individual. The level of impact is going to be considerably different on a woman of 1.56m than on a large men with a bourgondic lifestyle[7].

Examination

To examine the type of fracture an x-ray or/and a CT-scan must be taken[1].The radiograph gives a clear view of all the essential fundamental landmarks of the acetabulum.On a CT-scan you can see full 3D- reconstruction of the acetabulum, which facilitates the visualization of the fracture, the degree of the fracture and the associated fractures[6].

Medical management

Depending on the degree of hip instability and personal factors (associated fractures, age, general medical status), an operation can be the solution to many of these fractures. If the displacement of the fragment is greater than 3mm, operation is primarily suggested[7].These fractures often require an open reduction internal fixation (ORIF) to restore joint congruency and stabilization. For the operation they use screws and plates to fix the bone to prevent further displacement[8][9]With elderly patients, ORIF may not always be the best option because of possible osteoporosis. ORIF can be the solution to the fracture if the femoral head is still weight bearing and when the patient factors are no immediate cause to any complication. Patient factors include degree of underlying osteoporosis, comorbid medical conditions, preexisting degenerative joint disease (DJD), premorbid activity level, and baseline mental function[5]. In general total hip replacement will provide the best functional outcome in elderly patients with severe acetabulum fracture and osteoporosis[4].

Physical management

Usually this nonoperative treatment is recommended for patients with no displacements or minimal displacement like low anterior column or low transverse fractures, so the superior part of the acetabulum must be intact[10]. Early mobilization is necessary because prolonged recumbency can be life- threatening[5]. Conservative treatment includes pain control, functional physical therapy and radiographic follow-up[5]. Physical therapy include gait training, stabilization exercises and mobility training.

Patients who underwent an operation have to start with passive ROM exercises followed by active non weight bearing such as a series of flexion/extension . Partial weight-bearing with stepwise progression usually starts 6 weeks postoperatively and full weight bearing is eventually allowed at 10 weeks[11][7].

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